Photovoltaic cells are re-evaluated from the viewpoint of global environmental conservation due to the advantage of no pollution, and studies on photovoltaic cells as a next-generation clean energy source have been actively conducted.
As types of photovoltaic cells known until now, there are many various types such as a compound semiconductor solar cell, a dye-sensitized solar cell and an organic polymer solar cell, including a solar cell using single-crystalline or polycrystalline bulk silicon and a thin-film type solar cell using amorphous, microcrystalline or polycrystalline silicon.
A solar cell using the commercially available single-crystalline bulk silicon in the related art has not been actively utilized due to high manufacturing cost and installation costs.
In order to solve the cost problem, studies on a thin-film type solar cell using organic materials have been conducted, and various attempts for manufacturing a high-efficiency photovoltaic cell have been proposed.
The organic thin-film photovoltaic cell technology, which is a technology in which solar energy is converted into electrical energy using a polymer or low-molecular organic semiconductor, is a next-generation technology all including ultra-low price and versatile mass production characteristics such as a thin-film type device, a large-scale device and a flexible device by a roll-to-roll method based on a low cost and easiness of the manufacturing process, which are the biggest advantages of the organic material.
Typically, the organic photovoltaic cell includes a photoactive layer consisting of a junction structure of electron donor and electron acceptor materials.
When light is incident to the photoactive layer, an electron and hole pair is excited in the electron donor, and the separation of electrons and holes occurs as the electron moves to the electron acceptor. Accordingly, carriers produced by light produce electric power as the carriers are separated into electrons-holes, and then move to an external circuit.
For the aforementioned reasons, recent interests have been focused on a bulk heterojunction organic photovoltaic cell which is low in price and may be applied to a flexible substrate.
US Patent Application Publication No. 2006-0011233 discloses an organic photovoltaic cell in which poly(3-hexylthiophene (P3HT) as an electron donor and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor are used, and a photoactive layer is introduced by a spin-coating method, but the energy conversion efficiency thereof is not very high.